I have an early fuel injected 5.3 V12 that has quit running. I pulled off the fuel filter and it was blocked. I am trying to trouble shoot the system and have some questions to which I cannot find the answers in the Repair Operations Manual.
What is the function and the name of the “hockey puck” looking thing the fuel pump draws fuel through?
What is the hexagonal valve looking thing the fuel lines coming from the change over valve go through?
How do I determine which lines are COMING FROM the fuel tank and RETURNING TO the tank?
If anyone has anything to add in the diagnosis of my fuel system woes I would appreciate your input.
My factory manual is from 1972 so doesn’t cover the FI cars, and my Haynes manual doesn’t have pictures of those parts, but the 1976 parts catalogue has pictures but no names.
The hockey puck is part C.44420 and I think is probably a pressure regulator.
The hexagonal valve with 3 hoses is C.45603 and looks to me like a return valve opened by pressure in the return hose.
There are several pages of pictures of hoses and pipe lines. It appears that the supply to the engine runs on the right side of the car, and the return to the tank runs on the left side.
My '74 XJ12 carburetor car is that way.
If it is between the pump and the tank it is either an filter, David - or the changeover valve…
Is the combined ‘air bleed’ and ‘non-return’ valves. With the pump delivering pressure, fuel is going through the valve to the main filter and on to the fuel rail(s). When pump stops; the one-way valve close the fuel filter connection - retaining rail pressure. And opens the pump connection to the return line - to vent air from the pump…
The lines from the tank is in the boot underfloor - tank to changeover valve, to the pump, to the ‘hex’, to filter and to fuel rail. The return lines start at the fuel pressure regulator, back under the car - splitting in two, to the two return valves, ‘right’ and ‘left’ forward in the rear wheel wells. The up to the tanks near the filler necks…
Have you verified that the injectors are ‘clicking’ during cranking? The early FI used a special trigger unit in the distributor to trigger the injectors - and the trigger unit may have failed.
You have of course verified that you have spark while cranking? Use a spare spark plug connected to any plug lead to verify…
Frank, thanks for the info. I have confirmed the spark and timing by spraying some starter fluid in the intake and it will run, so I’m pretty confident It is a fuel problem. I am working through the possibilities and found the fuel filter blocked, so I am checking the fuel pump for pressure (as soon as my 100 psi gauge arrives). Meanwhile I am going through the changeover valve troubleshoot from the manual. I am also considering swapping out the remaining fuel lines for ethanol safe hose.
Because you have a plugged filter, I would start with the fuel tanks. Drain each tank through a strainer and see if there is crap in the tanks. Once the tanks are empty, you can check the small filter that slips up on the uptake line in the tank. You access that through the bottom of the tank after removing the cap that contains the tank plug. If you have crud in your tanks, you need to get that situation corrected first.
Good luck,
Phillip
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Checking fuel pressure is indeed the appropriate reaction to fuelling issues, David - it provides unambiguous result; it is either right or wrong. And will also reveal fuel restrictions. You have of coursed tried running on either tank…
Fuel return has no bearing on engine running - providing fuel is heard returning…
As an aside; starter fluid have lower ignition point - and theoretically may ignite by sparking too weak to ignite petrol…
Thank you to all who have responded. Here is what I have discovered and done with my XJ12C fuel supply system.
I found the big “soup can” sized filter was blocked solid. I drained the tanks and found about a quart of rusty water in the left tank and much more in the right tank. Assuming the tanks would be rust, I poured two gallons of white vinegar into each tank and let it sit overnight. Upon draining out the vinegar it flushed out some rust so I ran some more clean vinegar through with the plug out and flushed out most of the rust. At this point I could stick my finger up into the tank and it felt pretty clean. I removed the junk screens at he end of the fuel pick ups and sprayed carburetor cleaner through them. Before replacing them I used air pressure to blow out the lines.
Following a suggestion I found on another post on this site, I installed a auxiliary filter on each supply line before the changeover valve. Upon testing the valve I found it to be stuck in the default position. More carburetor cleaner got it to work properly.
While I was in there I replaced all the fuel lines both supply and return with E85 compliant barrier hose just for good measure. After hooking everything back up and testing for leaks, the beast fired right up and after a few moments settled down to a purr. I have yet to get it out and run it hard down the highway. I need to replace the tires since the ones are the car now are dated coded in 2000 I am not eager to do anything more than about 35 MPH on them.
David,
Congratulations on getting your 1975 XJ12C running again. It is interesting to note that a lot of cars that sat for a while do well after the tanks are flushed of debris and rust and fuel filters are replaced.
Job well done. No better feeling than employing a little common sense, before hand, and then working hard, on an unpleasant job, with the result of ending up with a great working system that will serve you for years. Life does not offer these opportunities for joy outcomes very often. But in the old car world, you are surrounded by these opportunities. The difficult part is, determining where to start.
Keep up the good work. Taking a car that is limited, by condition, to a top drive speed of 30 miles pure hour to a car that can easily cruise down the interstate is a wonderful thing. And the satisfaction does not diminish in time, it actually becomes a part of the car’s personality. As you work and improve each aspect of your car, you find yourself developing a deepening friendship with the machine through the process of building trust, the key element necessary to a strong relationship. You can trust your car to run the way you want it to and take you down the road with out reservation.
Enjoy the journey.Phillip
Thanks for the pats on the back. I have always said there is nothing that cannot be accomplished by someone who is willing to read and use their brain. I am mechanically inclined but do not claim to be a mechanic. With the shared knowledge I have found in this forum as well as a factory Repair Operations Manual I am forging forward with the restoration of a rare original XJ12C.
As soon as I figure out how to post photos I will do so. Any suggestions?
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To inspect the tanks you can empty the tanks and remove the tank units, David…
The point is that once started rust never sleeps, and resealing the tanks might be called for. Or, over time, tanks may rust clean through; filters may stop the rust entering the system, but will not prevent rusting …
Since I was in a rush to get he car running, I skipped removing the tanks. I agree boiling and sealing the tanks is the right way to go. If I had more time I would have. I figure since in the chemical process requires oxygen, I figure if I keep the tanks full and take car to avoid any water intrusion into the tanks, I can get by until I have to do a full restoration. BTW, I live in Arizona where I can still buy non-oxygenated, non-ethanol unleaded gasoline, so I am hoping I can get by for a while.
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Indeed, David - it’s the oxygen in water that cause the rusting. In principle; keeping the tanks full will prevent condensation and rusting - but not all petrol stations are all that ‘safe’ form water contamination…
